Amplifier devices with reflection absorption

ABSTRACT

A radio frequency (RF) amplifier configured to operate at a fundamental frequency (f 0 ) includes a transistor with a transistor output, an output matching network coupled to the transistor output, and a reflection absorption circuit. The output matching network includes an output path device connected between the transistor output and an output of the RF amplifier. The reflection absorption circuit is coupled between the transistor output and the output path device, and is configured to absorb reflected signal energy from the output path device.

TECHNICAL FIELD

Embodiments of the subject matter described herein relate generally toamplifiers, and more particularly to radio frequency (RF) poweramplifiers used in a variety of applications.

BACKGROUND

In general, amplifiers are used to increase the power of signals. Forexample, in some applications amplifiers can be used to convertlow-power radio frequency (RF) signals into larger RF signals fordriving the antenna of a transmitter. In such cases, amplifiers may beimplemented as part of an overall power amplifier used by an RFtransmission system.

One reoccurring issue in RF power amplifiers is excessive noise at theoutput of the RF power amplifier. When excessive noise is generated atthe output of the RF power amplifier that noise can then propagatethrough the system. The excessive noise can thus significantly impactthe overall performance of the system.

One type of noise that can be especially problematic for some RFapplication are called intermodulation product distortions, alsoreferred to as intermodulation distortion (IMD). Intermodulation productdistortion is a type of noise that results from the interaction andmodulation of two or more signals with different frequencies. Forexample, intermodulation product distortion can be caused bynonlinearities when amplifiers are operated near the compression point.Specifically, at compression a typical amplifier can no longer linearlyamplify the input signal properly and will thus distort the outputsignal. This distorted output signal will include additional harmoniccopies at multiples of the fundamental frequency but with lowermagnitudes levels. These harmonic copies can then interact and combinewith each other by addition and subtraction, thereby creating additionalsignals at other frequencies. These signals, generally calledintermodulation products, can fold back and interfere with othersignals, including adjacent allocated signals.

Of particular concern are the intermodulation products that fall withinthe operational RF band. If large enough these intermodulation productdistortions can result in impaired amplifier performance. For example,these intermodulation product distortions can impair wideband operationor reduce amplifier linearity, where amplifier linearity is ameasurement of how accurate the output signal is compared to the inputsignal applied to the input of the amplifier, particularly whengenerating high power. One type of application that is particularlysensitive to intermodulation product distortions are high power pulseamplifiers.

Therefore, there remains a need for amplifiers with reducedsusceptibility to noise, including intermodulation product distortions,particularity for high power RF applications.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the subject matter may be derived byreferring to the detailed description and claims when considered inconjunction with the following figures, wherein like reference numbersrefer to similar elements throughout the figures.

FIG. 1 is a schematic diagram of an amplifier in accordance with anexample embodiment;

FIGS. 2A and 2B are schematic diagrams of reflection absorption circuitsin accordance with example embodiments;

FIG. 3 is a top view of a portion of an amplifier in accordance with anexample embodiment;

FIG. 4 is a top view of a packaged amplifier in accordance with anexample embodiment;

FIG. 5 is a schematic diagram of a Doherty amplifier in accordance withan example embodiment; and

FIGS. 6A and 6B are graphs of exemplary spectrum plots.

DETAILED DESCRIPTION

The embodiments described herein can provide amplifiers, andparticularly radio frequency (RF) power amplifiers, with improvedperformance. Specifically, the embodiments described herein includeamplifiers with one or more reflection absorption circuits coupled toone or more transistor(s) outputs. These reflection absorption circuitscan be implemented to mitigate unwanted effects of signal reflections atthe transistor outputs that could otherwise lead to excessive noise,including intermodulation product distortions. By reducing the effectsof noise the reflection absorption circuits can increase amplifierlinearity in high frequency, high bandwidth, high power RF amplifiers.For example, the reflection absorption circuits can facilitate highpower pulse amplifiers with increased amplifier linearity.

In general, the reflection absorption circuits are configured to absorbsignal reflections at the transistor output in RF amplifiers used forhigh power amplification of the operational signals (i.e., theinformation-bearing signals intended for amplification andtransmission). As such, the reflection absorption circuits canfacilitate the use of certain bandwidth limited output path devices inthe output path of the RF amplifier. For example, the reflectionabsorption circuits can facilitate the use of certain packaged impedancetransformation devices as output path devices. As other examples, thereflection absorption circuits can facilitate the use of certainfrequency circulators as output path devices. In both cases thebandwidth limited devices can cause unwanted signal reflections thatcould propagate back to the transistor output and cause excessive noise,including intermodulation product distortions. The reflection absorptioncircuits provided in accordance with the embodiments described hereincan absorb these reflections and reduce the noise caused by thosereflections. As such, the reflection absorption circuits can facilitatethe use of these bandwidth limited output path devices in amplifierswhere they would otherwise cause excessive noise. As will be describedbelow, in some embodiments these bandwidth limited devices canfacilitate reduced device size and can in some cases reduce the noise atthe amplifier output by preventing the propagation of unwanted harmonicsignals to the amplifier output.

Turning now to FIG. 1, a schematic diagram of a portion of an exemplaryamplifier 100 is illustrated. The amplifier 100 includes a transistor102, an input matching network 104, a reflection absorption circuit 106,an output matching network 108, an RF input node 110, and an output loadnode 112 connected in series as shown. Although transistor 102 isreferred to in the singular sense, transistor 102 may include asingle-stage transistor, a two-stage transistor (e.g., a seriescombination of a driver amplifier transistor and a final-stage amplifiertransistor), or another transistor/amplifier topology.

The reflection absorption circuit 106 is coupled to an output of thetransistor 102. In general, the reflection absorption circuit 106 isconfigured to reduce noise at the output of the transistor 102 byselectively absorbing (e.g., dissipating and/or shunting to a groundreference node) the signal energy of certain reflected signal energy atthe output of the transistor 102.

Specifically, the reflection absorption circuit 106 can be configured toprovide a low impedance path to a ground reference node for signalenergy below a selected frequency (e.g., below the video bandwidthfrequencies of the amplifier 100). By providing this low impedance pathto a ground reference node for this signal energy, the reflectionabsorption circuit 106 can significantly reduce the noise and otherundesirable effects of that reflected signal energy. Conversely, thereflection absorption circuit 106 can be configured to present highimpedance to signal energy at selected higher frequencies to avoidnegatively impacting the operation of the amplifier 100 at those highfrequencies. For example, the reflection absorption circuit 106 can bedesigned to present an open circuit for high frequency RF signal energynear the fundamental frequency of operation of the amplifier (f₀). Asused herein, the term “near” with respect to a particular frequency(e.g., any of f_(B), f₀, or another frequency) may mean within 20percent of the particular frequency, for example.

In one embodiment, the reflection absorption circuit 106 is configuredto absorb reflected signal energy having frequencies below a basebandfrequency (f_(B)). To facilitate this, the reflection absorption circuit106 is configured to provide a low impedance profile for selectedfrequencies below the baseband frequency (f_(B)). For example, thereflection absorption circuit 106 can be configured to provide a lowimpedance profile and thus absorb reflected signal energy from about 0.2f_(B) to 0.8 f_(B).

As noted above, the reflection absorption circuit 106 can significantlyreduce the undesirable effects of reflected signal energy by providing alow impedance path to a ground reference node for that signal energy.For example, the low impedance path for reflected signal energy cansignificantly reduce the peak voltages generated at the output of thetransistor 102 by that reflected signal energy.

Specifically, the peak voltages generated by undesirable reflectedsignal energy are determined at least in part by current of thereflected signal energy and impedance seen by these currents as thereflected signal energy is dissipated and/or shunted to a referencenode. Thus, the low impedance path presented to the reflected signalenergy by the reflection absorption circuit 106 can significantly reducethe peak voltages generated by that reflected signal energy. Thisreduction in peak voltages caused by reflected signal energy can reducestresses on the transistor 102. Specifically, this reduction in peakvoltages can prevent the peak voltages from reaching beyond thebreakdown safe limits of the transistor 102. Finally, resistances in theabsorption reflection circuit 106 can dissipate and dampen the currentcaused reflected signal energy, providing additional protection to thetransistor 102.

The reflection absorption circuit 106 can be implemented to provide thisselective signal absorption with a variety of devices and circuits. Forexample, the reflection absorption circuits can be implemented with oneor more baseband termination circuits arranged in parallel. In suchembodiments each of the baseband termination circuits can be implementedto provide a low impedance profile for different frequency bandwidths.In such an embodiment each baseband termination circuit can include oneor more capacitors, inductors, and resistors, with the capacitors andinductors configured to resonate at a resonant frequency, and provide alow impedance path when resonating for signal energy at and near theresonant frequency. Detailed examples of such baseband terminationcircuits will be described below with reference to FIGS. 2A and 2B.

As described above, the reflection absorption circuit 106 is configuredto absorb (e.g., dissipate and/or shunt to a ground reference node)signal reflections at the output of the transistor 102 and as such canfacilitate high frequency, high bandwidth and high power RFapplications. Furthermore, this use of the reflection absorption circuit106 can facilitate the use of certain bandwidth limited devices in theoutput path of the amplifier 100. Such bandwidth limited devices canhave a relatively narrow effective bandwidth, where the effectivebandwidth of the device is the bandwidth for which the device isimplemented to operate and outside of which the device may undesirablyreflect a significant amount of signal energy.

For example, the reflection absorption circuit 106 can facilitate theuse of certain packaged devices in the implementation of amplifier 100.As one specific example, the reflection absorption circuit 106 canfacilitate the use of packaged impedance transformers as part of theoutput matching network 108. These packaged impedance transformers canprovide several advantages over other implementations but in many casespackaged impedance transformers have relatively narrower effectivebandwidths. For example, they can facilitate a reduction in device size.Specifically, the use of packaged impedance transformers can facilitatereduced printed circuit board (PCB) footprint for the amplifier 100.Additionally, a packaged impedance transformer can result in a cleaneroutput signal by not passing unwanted harmonic signals or otherundesirable signals to the output 112.

When used in the output matching network 108 of a high frequency and ahigh bandwidth amplifier such as amplifier 100, the relatively narroweffective bandwidth of the packaged impedance transformer can resultexcessive signal reflection as signal energy outside that narrowbandwidth may be reflected rather than passing through the impedancetransformer. As was described above, this reflected signal energy canpropagate back to the output of the amplifier 100, and can theregenerate potential noise and impair performance of the amplifier 100. Assuch, these packaged impedance transformers have generally not been usedin the output path of high frequency and high bandwidth amplifiers.Instead, they have generally been limited to the less demandingapplications, such as low frequency, narrow bandwidth amplifiers.Likewise, they have been limited to applications on the input of theside of the amplifier 100. As described above, the reflection absorptioncircuit 106 can absorb these reflections and thus facilitate the use ofpackaged impedance transformers and other bandwidth limited devices inthe output path of the amplifier 100.

Other examples of bandwidth limited devices that can be facilitated withthe use of reflection absorption circuit 106 include frequencycirculators. In general, frequency circulators are three terminaldevices that provide one way signal flow. Specifically, frequencycirculators allow signals to propagate from an input terminal to anoutput terminal but not in the opposite direction. However, somefrequency circulators also have a relatively narrow effective bandwidththat can also result in excessive signal reflection when used in theoutput path of high frequency and high bandwidth amplifiers. Asdescribed above, the reflection absorption circuit 106 can absorb thesereflections and thus facilitate the use of such frequency circulators inthe output path of the amplifier 100.

In a typical embodiment the transistor 102 is formed on a transistor dieand is encased in a device package that includes at least a first inputlead and a first output lead. In such an embodiment the reflectionabsorption circuit 106 can include at least a first inductance and atleast a first capacitance, where at least the first capacitance isformed on an integrated passive device (IPD) die. In such an embodimentthe IPD die can be encased inside the device package with the transistordie. In other embodiments, at least the first capacitance could beformed on a small printed circuit board, in or on a ceramic substrate(e.g., a low temperature co-fired ceramic (LTCC) substrate), or in or onanother type of substrate that can be encased inside the device packagewith the transistor die.

In yet other embodiments, the reflection absorption circuit 106 caninclude at least a first inductance and at least a first capacitance,where at least the first capacitance is coupled to a first output trace,where the first output input trace is coupled to the first output lead.Examples of such embodiments will be described with reference to FIG. 3.

As noted above, the reflection absorption circuit 106 is coupled to theoutput of the transistor 102. For example, the reflection absorptioncircuit 106 can be coupled to the output or current conducting terminal(e.g., a source terminal or collector terminal) of the transistor 102.

The transistor 102 can be implemented with a variety of different typesof transistors, including field effect transistors (FETs) and bipolarjunction transistors (BJTs), to give two non-limiting examples. In onespecific embodiment, the transistor 102 comprises a gallium nitride(GaN) field-effect transistor (FET). As more specific examples, variousIII-V field effect transistors may be used (e.g., a high electronmobility transistor (HEMT)), such as a GaN FET (or another type of III-Vtransistor, including a gallium arsenide (GaAs) FET, a gallium phosphide(GaP) FET, an indium phosphide (InP) FET, or an indium antimonide (InSb)FET). In other examples the transistor 102 may be implemented with aIII-V FET or with a silicon-based FET (e.g., a laterally-diffused metaloxide semiconductor (LDMOS) FET). In each of these cases the reflectionabsorption circuit 106 is coupled to the output of the transistor 102(e.g., the drain terminal) and is configured to absorb (e.g., dissipateor shunt to a ground reference node) certain reflected signal energy atthe output.

It should be noted that amplifier 100 is a simplified representation ofa portion of an amplifier, and in a more typical implementation theamplifier 100 would include additional features not illustrated inFIG. 1. For example, the amplifier 100 could include a variety of biascircuits. As other examples, the amplifier 100 could include additionaltransistors 102. Additionally, in some embodiments the amplifier 100could include additional amplification paths, with each path includingat least an additional reflection absorption circuit 106 and transistor102. Furthermore, the amplifier 100 could be implemented as a variety ofdifferent types of amplifiers, including class AB amplifiers. Asspecific examples, the amplifier 100 can be implemented as a single pathclass AB amplifier.

In other examples, the amplifier 100 can be implemented as part of amulti-path Doherty amplifier that uses a combination of class AB andclass C paths. In such an embodiment, a second instantiation ofamplifier 100 may be implemented in parallel with amplifier 100, thetransistor 102 can be implemented as a carrier transistor, and a secondinstantiation of transistor 102 (in the second instantiation ofamplifier 100) can be implemented as a peaking transistor. In such anamplifier a second instantiation of reflection absorption circuit 106(in the second instantiation of amplifier 100) can be implemented wherethe second reflection absorption circuit configured to absorb reflectedsignal energy at a second transistor output. An example of such anembodiment will be discussed in greater detail with reference to FIG. 5.

As noted above, a variety of different types of devices and circuits canbe used to implement the reflection absorption circuit 106. For example,the reflection absorption circuit 106 can be implemented with one ormore baseband termination circuits arranged in parallel. In general, abaseband termination circuit is a circuit configured to behave as abroadband low impedance circuit for frequencies below the amplifierbaseband, and behave as a high impedance circuit for signal energy atand near the fundamental frequency (f₀). In such embodiments, each ofthe baseband termination circuits can be implemented to provide a lowimpedance profile for a selected frequency range, and each of thebaseband termination circuits will thus absorb (e.g., dissipate and/orshunt to a ground reference node) reflected signal energy over itsselected frequency range. In some embodiments, multiple basebandtermination circuits can be implemented, with the multiple basebandtermination circuits configured with overlapping low impedance profiles(e.g., overlapping low impedance frequency ranges). When implementedtogether, these multiple baseband termination circuits provide acombined frequency range with a wider overall low impedance profile.Thus, reflected signal energy within the combined frequency range isabsorbed by the reflection absorption circuit 106, while signal energywith frequencies outside this combined frequency range are presentedwith a high impedance and are not absorbed.

Turning now to FIG. 2A, an exemplary reflection absorption circuit 200is illustrated. In general, the reflection absorption circuit 200 isconfigured to be coupled along a signal transmission path between atransistor output and an output matching network. So implemented, thereflection absorption circuit 200 can reduce noise at the output of atransistor by selectively absorbing (e.g., dissipating and/or shuntingto a ground reference node) certain reflected signal energy at theoutput of the transistor. Specifically, the reflection absorptioncircuit 200 provides a low impedance path to a ground reference node forreflected signal energy in selected frequency ranges.

In the example of FIG. 2A, the reflection absorption circuit 200includes two baseband termination circuits 202 and 203. Each of the twobaseband termination circuits 202 and 203 is configured to absorb (e.g.,dissipate and/or shunt to a ground reference node) reflected signalenergy over a different selected frequency range, where the differentpassband frequency ranges of circuits 202 and 203 are overlapping. Thus,when combined in parallel, the two baseband termination circuits 202 and203 can absorb reflected signal energy over a relatively large combinedfrequency bandwidth (e.g., a bandwidth that extends from a low frequencycutoff of circuit 202 to a high frequency cutoff of circuit 203).

Each of the two baseband termination circuits 202 and 203 includes afirst capacitive element 204, 214, a second capacitive element 205, 215,a first inductive element 206, 216, and a first resistive element 208,218, where an “element” may include a single component or a network ofcomponents. In this configuration, each of the baseband terminationcircuits 202 and 203 is configured to resonate at different selectedfrequencies and provide a low impedance path to a ground reference nodefor signal energy at these selected frequencies. Specifically, the firstcapacitive element 204, 214 and the first inductive element 206, 216will resonate at a first frequency, the second capacitive element 205,215 and the first inductive element 206, 216 will resonant at a secondfrequency, and the combination of first capacitive element 204, 214,second capacitive element 205, 215, and first inductive element 206, 216will resonate at a third frequency. Thus, each baseband terminationcircuit 202 and 203 can resonate at three different frequencies, and theoverall reflection absorption circuit 200 can thus resonant at sixdifferent frequencies. Taken together, this resonating at six differentfrequencies provides the reflection absorption circuit 200 with theability to absorb reflections over a relatively wide combined frequencyrange. Furthermore, this combined frequency range can be determined byimplementing appropriate values for the first capacitive elements 204,214, second capacitive elements 205, 215, and inductive elements 206,216.

For example, when the fundamental frequency of operation of theamplifier is between about 800 megahertz (MHz) and about 6.0 gigahertz(GHz), capacitance values of the capacitive elements 204, 214 may be ina range of about 1 nanofarads (nF) to about 10 nF, capacitance values ofthe capacitive elements 205, 215 may be in a range of about 82 nF toabout 120 nF, inductance values of the inductive elements 206, 216 maybe in a range of about 0.25 nanohenries (nH) to about 1 nH, and theresistance values of the resistive elements 208, 218 may be in a rangeof about 1 ohm to about 3.9 ohms. In other embodiments, the capacitive,inductive, and/or resistive values may be smaller or larger than theabove-listed ranges. In addition, the fundamental frequency of operationmay be less than 800 MHz or greater than 6.0 GHz.

Signal energy within this combined frequency bandwidth are dissipatedinto one of the corresponding resistive elements 208, 218 and/or shuntedto a ground reference node. In contrast, signal energy outside thiscombined frequency bandwidth is presented with relatively high impedanceand is thus not absorbed, but rather passed relatively unaffectedbetween the transistor output and the output matching network.

Turning now to FIG. 2B, an exemplary reflection absorption circuit 220is illustrated. Again, the reflection absorption circuit 220 isconfigured to be coupled between an output matching network and thetransistor output, and is implemented to reduce noise at the output of atransistor by selectively absorbing (e.g., dissipating and/or shuntingto a ground reference node) certain reflected signal energy at theoutput of the transistor.

In the example of FIG. 2B, the reflection absorption circuit 220includes four baseband termination circuits 219, 221, 222 and 223arranged in parallel. Each of the four baseband termination circuits219, 221, 222 and 223 is again configured to absorb reflected signalenergy over a different selected frequency range, where the differentpassband frequency ranges of circuits 219, 221, 222 and 223 areoverlapping. Thus, when coupled together in parallel, the four basebandtermination circuits 219, 221, 222 and 223 can absorb reflected signalenergy over a relatively large combined frequency bandwidth (e.g., abandwidth that extends from a low frequency cutoff of circuit 219 to ahigh frequency cutoff of circuit 223). By using the four basebandtermination circuits instead of two, the reflection absorption circuit220 can absorb (e.g., dissipate or shunt to a ground reference node)signal energy over a larger frequency range.

It should be noted that reflection absorption circuits 200 and 220 arejust two examples of reflection absorption circuits. For example,although the capacitive, inductive, and resistive elements are shown ina particular series-coupled order in FIGS. 2A and 2B (i.e., C-L-R),these elements may be arranged in different orders, in other embodiments(e.g., C-R-L, L-C-R, L-R-C, R-C-L, or R-L-C), and/or some or all of anyof these elements may be implemented using multiple components arrangedin various orders with both series- and/or parallel-connected components(e.g., C-L-C-R-L-R, to name just one example). Furthermore, other typesof resistor-inductor-capacitor (RLC) circuits can be implemented toabsorb reflected signal energy. As used herein, the term “RLC” circuitmeans a circuit that includes any arrangement of resistive, inductive,and capacitive components between two nodes.

Returning to FIG. 1, in general it is desirable to position thereflection absorption circuit 106 as physically close as possible to theoutput of the transistor 102. Specifically, it is generally desirablefor the reflection absorption circuit 106 to be physically close to thecurrent conducting terminal of the transistor 102 (e.g., the drainterminal when the transistor 102 is a FET). Locating the reflectionabsorption circuit 106 relatively far away from the output of thetransistor 102 could result in increased performance losses. Forexample, locating the reflection absorption circuit 106 relatively faraway can result in increased parasitic impedances that cause excessiveperformance losses due to the resulting impedance mismatching. A varietyof different techniques and structures can be use to implement thereflection absorption circuit 106 in a way that facilitates this closephysical proximity to the output of the transistor 102.

As noted above, the transistor 102 is typically formed on a transistordie (i.e., a semiconductor die that includes the transistor), where thetransistor die is then encased in a device package that includes one ormore input leads and output leads. The device package that includes thetransistor 102 can then be mounted on a substrate (e.g., a printedcircuit board). The printed circuit boards can include one or moreconductive traces, such as conductive input traces used to provide theelectrical coupling to the input of the transistor 102, and conductiveoutput traces used to provide the electrically coupling to the output ofthe transistor 102. Thus, when the device package that includes thetransistor 102 is mounted to the printed circuit board, the inputlead(s) of the device package are electrically coupled to the conductiveinput traces on the printed circuit board, and the output lead(s) of thedevice package are electrically coupled to the conductive output traceson the printed circuit board. Additionally, in some embodiments biasline traces are used to provide bias voltages to the inputs and/oroutputs of the transistor 102 (e.g., through the input/output leadsand/or through dedicated bias leads).

In some embodiments, the reflection absorption circuit 106 can beincorporated with the output traces on the printed circuit board toprovide a close proximity between the reflection absorption circuit 106and the output of the transistor 102. In such embodiments the resistive,capacitive and inductive elements that implement the reflectionabsorption circuit can be formed on or attached to the printed circuitboard in close proximity to the transistor 102. For example, one or morediscretely packaged resistors, capacitors and/or inductors can bemounted on the printed circuit board in a way that connects thoseelements to the output traces in close proximity to the output of thetransistor 102 (or to the output lead of the device package). In otherembodiments, one or more discretely packaged resistors, capacitorsand/or inductors can be mounted on the printed circuit board in a waythat connects those elements to the bias line traces in close proximityto the output of the transistor 102. In other embodiments the resistive,capacitive and/or inductive elements can be formed from one or moreadditional traces on the printed circuit board, where those additionaltraces are again in close proximity to the output of the transistor 102.

Turning now to FIG. 3, a schematic view of a portion of an amplifier 300is illustrated. The amplifier 300 includes packaged transistor device302 and packaged impedance transformers 308 mounted to a printed circuitboard 303. The packaged impedance transformers 308 each represent abandwidth limited output path device in the output path of the amplifier300, which could cause unwanted signal reflections that could propagateback to the transistor output and cause excessive noise, includingintermodulation product distortions, in the absence of reflectionabsorption circuits implemented on the printed circuit board 303, asdescribed below. The reflection absorption circuits provided inaccordance with the embodiments described herein can absorb suchreflections and reduce the noise caused by those reflections. As such,the reflection absorption circuits can facilitate the use of thepackaged impedance transformers 308 (or other bandwidth limited outputpath devices, including but not limited to discretely packagedcirculators) in the output paths amplifiers by reducing or substantiallyeliminating undesirable noise caused by reflections from the inputs ofthe packaged impedance transformers 308.

In this embodiment the packaged transistor device 302 includes twoencased transistors, two input leads (on the left side of the device302), and two output leads (on the right side of the device 302. Eachencased transistor has its own input (i.e., the two encased transistorsare implemented in parallel with each other, each connected between adifferent input/output lead pair). The printed circuit board 303includes a plurality of conductive traces or portions, including twooutput traces 304, bias line portion 306, a combiner trace 310, and aground reference trace 318 (corresponding to a ground reference node).For example, the traces 304, 310, 318 may be implemented as patternedportions of a conductive layer on a top surface of the printed circuitboard 303. Each of the output traces 304, in combination with an outputlead and conductive structures (e.g., wirebonds) inside the packagedtransistor device 302) provides an electrical connection to the output(e.g., the drain terminal) of a corresponding transistor in the packagedtransistor device 302. Specifically, each of the output traces 304 iscoupled to a package output lead on the packaged transistor device 302.Furthermore, each of the output traces 304 is coupled to a differentpackage lead on a corresponding one of the packaged impedancetransformers 308. Thus, the output traces 304 provide the electricalconnection between the output terminals of the transistors and thepackaged impedance transformers 308. Finally, the output traces 304 eachinclude a bias line portion 306 for providing bias voltages to theoutputs of the transistors. The combiner trace 310 combines the outputsof the two transistors (or more specifically the outputs of the twopackaged impedance transformers 308) and provides a phase delay to atleast one of the amplification paths, as will be described in greaterdetail below. The ground reference trace 318 may be electricallyconnected to a system ground reference voltage.

Each packaged impedance transformer 308 is a implemented as a surfacemount package (e.g., a QFN or other surface mount package) that issurface mounted to the printed circuit board 303. Each packagedimpedance transformer 308 includes a first terminal (electricallycoupled to one of traces 304), a second terminal (electrically coupledto a part of trace 310), and an internal impedance transformationcircuit coupled between the first and second terminals of the impedancetransformer 308.

In accordance with the embodiments described herein, a reflectionabsorption circuit 320, 340 is coupled to the output of each of thetransistors in the packaged transistor device 302, and each reflectionabsorption circuit 320, 340 is implemented on the printed circuit board303 (e.g., using discrete, surface-mounted, passive components). Morespecifically, each reflection absorption circuit 320, 340 iselectrically connected to the output path of the transistor at aconnection point between the transistor output (or an output lead ofdevice 302) and an input terminal of a packaged impedance transformer308. In the illustrated embodiment, each of the reflection absorptioncircuits 320, 340 includes two parallel circuits coupled between thetransistor output and a ground reference trace 318. The two parallelcircuits of reflection absorption circuit 320 include a first seriescircuit coupled between bias line portion 306 of trace 304 and 318 thatincludes a resistive element 328 (e.g., resistive element 208),capacitive element 324 (e.g. capacitive elements 204, 205), andinductive element 326 (e.g., capacitive element 206), and a secondseries circuit coupled between bias line portion 306 of trace 304 and318 that includes a resistive element 338 (e.g., resistive element 218),capacitive element 334 (e.g. capacitive elements 214, 215), andinductive element 326 (e.g., capacitive element 316). The two parallelcircuits of reflection absorption circuit 340 include a first seriescircuit coupled between bias line portion 306 of traces 304 and 318 thatincludes a resistive element 348 (e.g., resistive element 208),capacitive element 344 (e.g. capacitive elements 204, 205), andinductive element 346 (e.g., capacitive element 206), and a secondseries circuit coupled between bias line portion 306 of trace 304) and318 that includes a resistive element 358 (e.g., resistive element 218),capacitive element 354 (e.g. capacitive elements 214, 215), andinductive element 356 (e.g., capacitive element 316).

In this particular embodiment each of the resistive element 328, 338,348, 358, capacitive element 324, 334, 344, 354, and inductive element326, 336, 346, 356 are formed as separate discrete devices (e.g.,surface mount devices) that are mounted to the printed circuit board303. More specifically, first and second terminals of each element 328,338, 348, 358, 324, 334, 344, 354, 326, 336, 346, 356 are connected(e.g., soldered or conductively adhered) to conductive traces on the topsurface of printed circuit board 303, and one of the conductive traces318 is coupled to a ground reference node at a bottom surface of theprinted circuit board 303 through conductive vias that extend betweenthe top and bottom surfaces of the printed circuit board 303.Accordingly, the elements 312, 314, 316 are connected in series betweenthe bias line portion 306 of the conductive output trace 304. However,in other embodiments one or more of these elements could be made fromconductive traces or in some other manner. Further, the resistive,capacitive, and inductive elements 328, 338, 348, 358, 324, 334, 344,354, 326, 336, 346, 356 could be interconnected in a different orderfrom that shown in FIG. 3. Further still, although each reflectionabsorption circuit 320, 340 is shown to include two parallel RLCcircuits, each reflection absorption circuit 320, 340 alternativelycould include a single RLC circuit, or more than two parallel RLCcircuits (e.g., four parallel RLC circuits, as shown in FIG. 2B, or someother number of parallel RLC circuits).

It should be noted that in the amplifier 300 the reflection absorptioncircuits 320, 340 are located in close physical proximity to the outputsof the transistors encased within the packaged transistor device 302. Asused herein, “in close proximity”, when referring to the proximity of areflection absorption circuit (or more specifically a first terminal ofa first series element of a reflection absorption circuit) means withinabout 22 electrical degrees to about 45 electrical degrees (˜between 300mils to 600 mils) of the output of a transistor, although “in closeproximity” alternatively may mean a smaller or larger distance, as well.In this particular embodiment this is accomplished by coupling a firstseries element (e.g., capacitive element 328, 338, 348, 358) directly tothe bias line portion 306 of the conductive output trace 304.Furthermore, the reflection absorption circuits 320, 340 areelectrically coupled to nodes between the output of the transistors andthe inputs to the packaged impedance transformers 308. Providing thereflection absorption circuits 320, 340 between the output of thetransistors and the inputs to the packaged impedance transformers 308allows the reflection absorption circuits 320, 340 to absorb signalenergy in reflections from the inputs to those packaged impedancetransformers 308. This allows such packaged impedance transformers 308to be used as part of the output matching network of the amplifier evenwhen the packaged impedance transformers 308 are bandwidth limited, andwithout causing degradation in various other amplifier performancecriteria.

It should be noted that the amplifier 300 is just one exampleimplementation, and that other implementations are possible. Forexample, in some cases one or more elements of the reflection absorptioncircuits 320, 340 can be packaged with the transistors in the packagedtransistor device 302. In such embodiments these elements of thereflection absorption circuits can be formed on or attached to aseparate die or substrate (e.g., an IPD die, small PCB, LTCC substrate,and so on), and then packaged in the same package as the transistordies. Inductive elements could be formed from wirebonds, or in/on theaforementioned dies or substrates. In other embodiments one or more ofthese elements of the reflection absorption circuits could be integratedwithin and/or connected to the same die as the transistor. The term“package”, “package device”, or “packaged transistor device”, as usedherein means a collection of structural components (e.g., including aflange or other package substrate) to which the primary electricalcomponents (e.g., input and output leads, transistor dies, IPD dies, andvarious electrical interconnections) are coupled and/or encased. Thepackage, package device, or packaged transistor device is thus adistinct device that may be mounted to a printed circuit board or othersubstrate that includes other devices and portions of a circuit. Asspecific examples, the package, package device, or packaged transistordevice can comprise an air cavity or over-molded package having asuitable package substrate, input lead(s), and output lead(s). Inaddition, the package, packaged device, or packaged transistor devicecould be implemented using other packaging configurations than thoseshown in the figures, such as but not limited to no-leads packages(e.g., quad flat no-leads, QFN), or other package types.

Turning now to FIG. 4, a top view of a portion of an exemplary amplifier400 that is implemented within a discrete device package 402 isillustrated. The package 402 includes a package substrate 403, inputleads 404, output leads 406 and biasing leads 408. The package substrate403 (e.g., flange or other substrate with a conductive top surface thatserves as a ground plane) serves as a structural component to whichvarious semiconductor dies are mounted or otherwise connected. Thedevice package 402 also may include an isolator that electricallyisolates the package substrate or flange from the leads 404, 406 and408, or alternatively may include encapsulation that provides suchelectrical isolation. The package 402 may be an air-cavity package or aplastic encapsulated (overmolded) package.

In this example, amplifier 400 implements two amplification paths, witheach amplification path including an input IPD die 412, a transistor die410, and an output IPD die 414, all encased together in one package 402.Each transistor die 410 can include one ore more integrated transistors(e.g., silicon-based or III-V-based FETs). In one embodiment in whichthe amplifier 400 forms a portion of a Doherty amplifier (as describedin more detail in conjunction with FIG. 5), one of the transistor dies410 can function as a carrier transistor, and the other transistor die410 can function as one or more peaking transistors, with eachtransistor formed on a corresponding semiconductor die. Likewise, insome embodiments portions of input matching networks can be implementedon the input IPD dies 412, and portions of output matching networks canbe implemented on the output IPD dies 414.

In this implementation the input leads 404 are each configured toreceive an RF signal (e.g., from a signal divider that is implemented ona PCB to which the package 402 is coupled), and bond wire arrays 420,which may form portions of the input matching components, connect theinput leads 404 to input IPD dies 412, and connect the IPD dies 412 tothe control terminals (e.g., gates) of the transistors within transistordies 410. Likewise, various bond wire arrays 420, which may formportions of the output matching components, connect the output IPD dies414 to the output leads 406, and connect the output IPD dies 414 to theoutput terminals (e.g., drain terminals) of the transistors withintransistor dies 410.

In accordance with the embodiments described herein, one or morecomponents of reflection absorption circuits (e.g., reflectionabsorption circuits 106, 200, 220, 320, 340) are included inside thepackage 402. For example, various resistive, capacitive and inductiveelements can be integrated within, formed on, or attached to the outputIPD dies 414. Furthermore, various discrete devices can be additionallyincluded inside the package 402. Finally, in some embodiments inductiveelements can be provided with the bond wire arrays 420.

As was described, in some implementations the reflection absorptioncircuits described above can be included in Doherty amplifiers. Ingeneral, a Doherty amplifier divides an input RF signal and usesamplifiers of different classes to amplify the divided parts of the RFsignal, after which the amplified signals are combined. Specifically, aDoherty amplifier typically uses a carrier amplifier in parallel withone or more peaking amplifiers, with the carrier amplifier used toamplify relatively low power input signals, and both the carrieramplifier and the one or more peaking amplifiers used to amplifyrelatively high power input signals (e.g., the peaks of the signal). Insuch an implementation, the carrier amplifier is typically biased tooperate as a class AB driver, and the peaking amplifier(s) are biased tooperate as class C drivers.

In such an embodiment, the carrier amplifier can comprise one or moretransistors (e.g., including a driver transistor and a final stagetransistor, or just a final stage transistor), and the peaking amplifiercan comprise one or more other transistors (e.g., including a drivertransistor and a final stage transistor, or just a final stagetransistor). Thus, single stage (e.g., single transistor) carrier andpeaking amplifiers can be used in some embodiments, and otherembodiments can include multiple-stage amplifiers (e.g., in which eachamplification path includes a driver amplifier (transistor) and afinal-stage amplifier (transistor) coupled in series).

In a typical Doherty implementation, when the input RF signal is atrelatively low signal levels, the carrier amplifier operates near itscompression point and thus with high efficiency, while the peakingamplifier(s) are not operating. Thus, at relatively low signal levelsthe Doherty amplifier can provide both high efficiency and goodlinearity. Then, when higher signal levels occur, the carrier amplifiercompresses, and one or more of the peaking amplifier(s) start to operateto “top up” the resulting output signal. Thus, the peaking amplifier(s)provide the ability to achieve high power output during times of highinput signal levels. Thus, the carrier and peaking amplifiers of theDoherty amplifier together can provide relatively high power output andhigh efficiency. Stated another way, Doherty amplifiers thus can combineclass AB and class C amplifiers in a way that maintains linearity whileproviding high power efficiency, and can further provide a high poweroutput.

Turning now to FIG. 5, a circuit diagram representing a portion of anexemplary amplifier 500 is illustrated. In this illustrated embodiment,the amplifier 500 is a Doherty amplifier that receives an RF inputsignal at the RF input 517 and drives an amplified signal to a loadoutput 518. The amplifier 500 includes a carrier amplifier 502, apeaking amplifier 504, a divider 506, a first packaged impedancetransformer 508, a second packaged impedance transformer 510, anadditional impedance transformer and/or phase shifter 512, a combiningnode 514, a first reflection absorption circuit 550, and a secondreflection absorption circuit 560.

In a typical embodiment, the divider 506 receives an RF signal andgenerates two output signals that are 90 degrees out of phase with eachother. These two outputs correspond to the first signal and secondsignal that are applied to the carrier amplifier 502 and peakingamplifier 504 respectively. The two outputs can be in the form ofequal-power or unequal-power signals. The 90 degree phase difference canbe provided by a phase delay element that applies a phase shift of about90 degrees to the second signal before outputting the second signal tothe peaking amplifier 504. The 90 degree difference in phase allows theoutput of the peaking amplifier 504 to be in step with the carrieramplifier 502 output when combined at the combining node 514.

The amplifier 500 receives and amplifies the first signal and the phasedelayed second signal, combines the amplified first and second signalsin phase, and drives the combined signal to a load output 518. Thecarrier amplifier 502 includes one or more carrier transistors, and thepeaking amplifier 504 includes one or more peaking transistors, and theoutputs of the carrier and peaking transistors are coupled to packagedimpedance transformers 508, 510, transformer/phase shifter 512, andcombining node 514.

The packaged impedance transformers 508, 510 (e.g., packaged impedancetransformers 308, FIG. 3) are configured to transform the impedance atthe output of the transistors to one acceptable for the load. Forexample, the packaged impedance transformers 508, 510 can be impedanceincreasing transformers that increase the final output impedance ofamplifier to a desired level. In one specific embodiment, the packagedimpedance transformers 508, 510 comprise 4 ohm to 50 ohm transformers.

The packaged impedance transformers 508, 510 typically include one ormore passive devices (inductors, capacitors, resistors) that are packedtogether in a semiconductor device package. Again, the “package” in thiscontext means a collection of structural components (e.g., including aflange or other package substrate) to which the primary electricalcomponents (e.g., input and output leads, passive devices, IPD dies, andvarious electrical interconnections) are coupled and/or encased. Thepackaged impedance transformers 508, 510 are thus devices that may bemounted to a PCB or other suitable substrate. Again, packaged impedancetransformers 508, 510 can provide several potential advantages, but havegenerally not been used in output matching networks for high frequencyhigh bandwidth amplifiers because of limitations in their effectivebandwidth. When used with various embodiments of the inventive subjectmatter, the packaged impedance transformers 508, 510 can facilitate areduction in overall amplifier size (or footprint) without significantperformance degradation due to signal reflections produced at the inputsto the packaged impedance transformers 508, 510.

Conceptually, the transformer/phase shifter 512 can be considered toinclude a ¼ wave transformer. The transformer/phase shifter 512 andcombining node 514 function as combiner that combines the outputs of thecarrier amplifier 502 and peaking amplifier 504 such that the combinedoutput can be delivered to the load output 518. To facilitate this, thecombining node 514 is coupled to the load output 518. Thetransformer/phase shifter 512 may include a ¼ wave transformer, whichprovides a 90 degree phase shift to the output of the carrier amplifier502 and thus facilitates the in-phase combining of that output with theoutput of the peaking amplifier 504. The transformer/phase shifter 512also provides an impedance inversion between the outputs of the carrieramplifier 502 and the peaking amplifier 504. During operation, theimpedance inversion effectively changes the impedance seen by thecarrier amplifier 502 to provide an optimal load to the carrieramplifier 502 at and around the operational frequency.

In a typical Doherty implementation, the carrier amplifier 502 is biasedto operate as a class AB amplifier, and is used to drive the main bodyof the output signal. Conversely, the peaking amplifier 504 is biased tooperate as a class C amplifier, and is used to drive the peaks of theoutput signal. This use of the two amplifiers 502 and 504 as class ABand class C amplifiers with outputs that are combined together canprovide both relatively high power output and high efficiency.

In a typical embodiment, the carrier amplifier 502 and peaking amplifier504 would be implemented with suitable RF-capable transistors withrelatively high power capability. For example, the carrier amplifier 502and peaking amplifier 504 can be implemented with III-V type transistors(e.g., Gallium Nitride (GaN) transistors), silicon-based transistors(e.g., LDMOS FETs), or other types of transistors.

In accordance with the embodiments described herein, the Dohertyamplifier 500 includes a first reflection absorption circuit 550 and asecond reflection absorption circuit 560. The reflection absorptioncircuit 550 (e.g., circuit 160, 200, 220) is coupled to a node along afirst amplification path between an output of a transistor in thecarrier amplifier 502 and the packaged impedance transformer 508.Likewise, the reflection absorption circuit 560 (e.g., circuit 160, 200,220) is coupled to a node along a second amplification path between anoutput of a transistor in a peaking amplifier 504 and the packagedimpedance transformer 510. Again, each of these reflection absorptioncircuits 550, 560 is configured to absorb (e.g., dissipate or shunt to aground reference node) reflected signal energy from the packagedimpedance transformers 508, 510 and thus reduce the noise potentiallyassociated with such signal energy.

In this particular embodiment the reflection absorption circuits 550,560 are configured to absorb (e.g., dissipate or shunt to a groundreference node) signal energy that might be reflected back from theinputs of the packaged impedance transformers 508, 510. In thisparticular embodiment this is accomplished by coupling the reflectionabsorption circuit 550 between the first packaged impedance transformer508 and the output of the carrier amplifier 502. Likewise, thereflection absorption circuit 560 is coupled between the second packagedimpedance transformer 510 and the output of the peaking amplifier 504.Providing the reflection absorption circuits 550, 560 between the outputof the amplifiers 502, 504 and the packaged impedance transformers 508,510 allows the reflection absorption circuits to absorb reflections fromthose packaged impedance transformers 508, 510. Again, this allows suchpackaged impedance transformers 508, 510 to be used in the Dohertyamplifier 500 even when the packaged impedance transformers 508, 510 arebandwidth limited.

As described above, the use of the reflection absorption circuits (106,200, 220, 320, 340, 550, 560) can reduce the noise at the output of theamplifier (100, 300, 500) and thus provide improved amplifierperformance. In some embodiments this can include a reduction in a typeof noise referred to as intermodulation product distortions orintermodulation distortion. In general, intermodulation productdistortions are unwanted modulations of signals that include two or morefrequencies. Such intermodulation product distortions can be generatedat harmonic frequencies, but also at sum and difference frequencies ofthe original frequencies and sum and difference frequencies of themultiples of the original frequencies.

Turning now to FIGS. 6A and 6B, graphs 600 and 650 show spectrum plotsof exemplary amplified RF signals. These spectrum plots show the poweroutput versus frequency for the effective bandwidth of an exemplary highfrequency, high bandwidth, high power RF amplifier.

Graph 600 shows a spectrum plot for the output of an amplifier thatfails to mitigate effects of the significant unwanted intermodulationproduct distortions. Specifically, graph 600 shows intermodulationproduct distortions 602 and 604 that occur between two exemplary tonesignal frequencies F1 and F2 in an amplifier that does not includereflection absorption circuits in accordance with the embodimentsdescribed herein. Such large intermodulation product distortions can becaused at least in part by signal energy reflecting back toward theoutput of the transistor. In this illustrated example the largeintermodulation product distortions 602 and 604 that fall between thetone signal frequencies F1 and F2 are within the operational RF bandthus can greatly impair wideband operation and reduce amplifierlinearity.

Graph 650 shows a spectrum plot for the output of an exemplary amplifierthat includes reflection absorption circuits that reduce (e.g. dissipateand/or shunt to a ground reference node) signal energy associated withunwanted intermodulation product distortions. Specifically, graph 650shows that the intermodulation product distortions between tone signalfrequencies F1 and F2 have been significantly reduced by the addition ofthe reflection absorption circuits in accordance with the embodimentsdescribed herein. This reduction in noise in general and intermodulationproduct distortions in particular can significantly improve theperformance of the amplifier. Specifically, by reducing theintermodulation product distortions between F1 and F2 thisimplementation of reflection absorption circuits can increase amplifierlinearity in high frequency, high bandwidth, high power RF amplifiers.For example, the reflection absorption circuits can facilitate highpower pulse amplifiers with increased amplifier linearity.

In one embodiment, a radio frequency (RF) amplifier is provided, the RFamplifier configured to operate at a fundamental frequency (f₀), the RFamplifier comprising: a first transistor, wherein the first transistorincludes a first transistor input and a first transistor output; a firstoutput matching network coupled to the first transistor output, thefirst output matching network including a first output path deviceconnected between the first transistor output and an output of the RFamplifier, the first output path device having a first effectivebandwidth; and a first reflection absorption circuit, the firstreflection absorption circuit coupled between the first transistoroutput and the first output path device and configured to absorbreflected first signal energy from the first output path device.

In another embodiment, a radio frequency (RF) amplifier is provided, theRF amplifier configured to operate at a fundamental frequency (f₀), theRF amplifier comprising: a printed circuit board with a first outputtrace; a first transistor, wherein the first transistor includes a firsttransistor output connected to the first output trace; a first outputmatching network coupled to the first transistor output through thefirst output trace, the first output matching network including a firstpackaged impedance transformer mounted to the printed circuit board, thefirst packaged impedance transformer having a first effective bandwidth;and a first reflection absorption circuit, the first reflectionabsorption circuit coupled between the first transistor output and thefirst packaged impedance transformer and configured to absorb reflectedfirst signal energy from the first packaged impedance transformer,wherein the first reflection absorption circuit includes a firstcapacitor and a first inductor coupled to the first output trace of theprinted circuit board.

In another embodiment, a Doherty radio frequency (RF) amplifierconfigured to amplify RF signals having a fundamental frequency (f₀) anda baseband frequency (f_(B)) is provided, the RF amplifier comprising: adivider configured to receive the RF signals and to divide the RFsignals into first and second RF signals provided at a first divideroutput and a second divider output; a first transistor coupled to thefirst divider output, wherein the first transistor includes a firsttransistor input and a first transistor output, and wherein the firsttransistor is a carrier amplifier in the Doherty RF amplifier; a firstoutput matching network coupled to the first transistor output, thefirst output matching network including a first impedance transformer,the first impedance transformer having a first effective bandwidth; afirst reflection absorption circuit, the first reflection absorptioncircuit coupled between the first transistor output and the firstimpedance transformer and configured to absorb reflected first signalenergy from the first impedance transformer; a second transistor coupledto the second divider output, wherein the second transistor includes asecond transistor input and a second transistor output, and wherein thesecond transistor is a peaking amplifier in the Doherty RF amplifier; asecond output matching network coupled to the second transistor output,the second output matching network including a second impedancetransformer, the second impedance transformer having a second effectivebandwidth; a second reflection absorption circuit, the second reflectionabsorption circuit coupled between the second transistor output and thesecond impedance transformer and configured to absorb reflected secondsignal energy from the second impedance transformer; and a combiner, thecombiner coupled to the first transistor output and the secondtransistor output.

The preceding detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,or the following detailed description.

Furthermore the connecting lines shown in the various figures containedherein are intended to represent exemplary functional relationshipsand/or physical couplings between the various elements. It should benoted that many alternative or additional functional relationships orphysical connections may be present in an embodiment of the subjectmatter. In addition, certain terminology may also be used herein for thepurpose of reference only, and thus are not intended to be limiting, andthe terms “first”, “second” and other such numerical terms referring tostructures do not imply a sequence or order unless clearly indicated bythe context.

As used herein, a “node” means any internal or external reference point,connection point, junction, signal line, conductive element, or thelike, at which a given signal, logic level, voltage, data pattern,current, or quantity is present. Furthermore, two or more nodes may berealized by one physical element (and two or more signals can bemultiplexed, modulated, or otherwise distinguished even though receivedor output at a common node).

The foregoing description refers to elements or nodes or features being“connected” or “coupled” together. As used herein, unless expresslystated otherwise, “connected” means that one element is directly joinedto (or directly communicates with) another element, and not necessarilymechanically. Likewise, unless expressly stated otherwise, “coupled”means that one element is directly or indirectly joined to (or directlyor indirectly communicates with, electrically or otherwise) anotherelement, and not necessarily mechanically. Thus, although the schematicsshown in the figures depict several exemplary arrangements of elements,additional intervening elements, devices, features, or components may bepresent in other embodiments of the depicted subject matter.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or embodiments described herein are not intended tolimit the scope, applicability, or configuration of the claimed subjectmatter in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the described embodiment or embodiments. It should beunderstood that various changes can be made in the function andarrangement of elements without departing from the scope defined by theclaims, which includes known equivalents and foreseeable equivalents atthe time of filing this patent application.

What is claimed is:
 1. A radio frequency (RF) amplifier configured tooperate at a fundamental frequency (f₀), the RF amplifier comprising: afirst transistor, wherein the first transistor includes a firsttransistor input and a first transistor output; a first output matchingnetwork coupled to the first transistor output, the first outputmatching network including a first output path device connected betweenthe first transistor output and an output of the RF amplifier, the firstoutput path device having a first effective bandwidth; and a firstreflection absorption circuit, the first reflection absorption circuitcoupled between the first transistor output and the first output pathdevice and configured to absorb reflected first signal energy from thefirst output path device, wherein the first reflection absorptioncircuit comprises a first baseband termination circuit and a secondbaseband termination circuit in parallel with the first basebandtermination circuit.
 2. The RF amplifier of claim 1, wherein the firstbaseband termination circuit is configured to provide a low impedancepath for signal energy at first frequencies below a baseband frequency(f_(B)) and wherein the second baseband termination circuit isconfigured to provide a low impedance path for signal energy at secondfrequencies below the baseband frequency.
 3. The RF amplifier of claim1, wherein the first baseband termination circuit includes a firstcapacitor and a first inductor coupled in series between the firsttransistor output and a ground reference node, the first capacitor andthe first inductor configured to resonate at a first frequency below abaseband frequency (f_(B)).
 4. The RF amplifier of claim 3, wherein thefirst capacitor and the first inductor are coupled to a first outputtrace on a printed circuit board to which the first transistor and thefirst output path device are coupled.
 5. The RF amplifier of claim 2,wherein the first frequency below the baseband frequency (f_(B))comprises a frequency between 0.2 f_(B) and 0.8 f_(B).
 6. The RFamplifier of claim 1, wherein the first output path device comprises apackaged impedance transformer.
 7. The RF amplifier of claim 6, whereinthe packaged impedance transformer comprises a surface mount package. 8.The RF amplifier of claim 1, wherein the first output path devicecomprises a packaged impedance transformer configured to increase animpedance to 50 ohms.
 9. The RF amplifier of claim 1, wherein the firstoutput path device comprises a frequency circulator.
 10. A radiofrequency (RF) amplifier configured to operate at a fundamentalfrequency (f₀), the RF amplifier comprising: a first transistor, whereinthe first transistor includes a first transistor input and a firsttransistor output, wherein the first transistor is formed on a firsttransistor die, and wherein the first transistor die is encased in adevice package that includes at least a first input lead and a firstoutput lead; a first output matching network coupled to the firsttransistor output, the first output matching network including a firstoutput path device connected between the first transistor output and anoutput of the RF amplifier, the first output path device having a firsteffective bandwidth; and a first reflection absorption circuit, thefirst reflection absorption circuit coupled between the first transistoroutput and the first output path device and configured to absorbreflected first signal energy from the first output path device, whereinthe first reflection absorption circuit includes at least a firstinductance and a first capacitance, and wherein the first capacitance isformed on a first integrated passive device (IPD) die, and wherein thefirst IPD die is encased in the device package with the first transistordie.
 11. The RF amplifier of claim 1, wherein the RF amplifier comprisesa Doherty amplifier, and wherein the first transistor is a carriertransistor in the Doherty amplifier, and wherein the RF amplifierfurther comprises: a second transistor, wherein the second transistor isa peaking transistor in the Doherty amplifier, and wherein the secondtransistor includes a second transistor input and a second transistoroutput; a second output matching network coupled to the first transistoroutput, the second output matching network including a second outputpath device connected between the second transistor output and theoutput of the RF amplifier, the second output path device having asecond effective bandwidth; and a second reflection absorption circuit,the second reflection absorption circuit coupled between the secondtransistor output and the second output path device and configured toabsorb reflected second signal energy from the second output pathdevice.
 12. A radio frequency (RF) amplifier configured to operate at afundamental frequency (f₀), the RF amplifier comprising: a printedcircuit board with a first output trace; a first transistor, wherein thefirst transistor includes a first transistor output connected to thefirst output trace; a first output matching network coupled to the firsttransistor output through the first output trace, the first outputmatching network including a first packaged impedance transformermounted to the printed circuit board, the first packaged impedancetransformer having a first effective bandwidth; and a first reflectionabsorption circuit, the first reflection absorption circuit coupledbetween the first transistor output and the first packaged impedancetransformer and configured to absorb reflected first signal energy fromthe first packaged impedance transformer, wherein the first reflectionabsorption circuit includes a first capacitor and a first inductorcoupled to the first output trace of the printed circuit board, andwherein the first reflection absorption circuit comprises a firstbaseband termination circuit and a second baseband termination circuitin parallel with the first baseband termination circuit.
 13. The RFamplifier of claim 12, wherein the first baseband termination circuit isconfigured to provide a low impedance path for signal energy at firstfrequencies below a baseband frequency (f_(B)) and wherein the secondbaseband termination circuit is configured to provide a low impedancepath for signal energy at second frequencies below the basebandfrequency.
 14. The RF amplifier of claim 13, wherein the firstfrequencies below the baseband frequency (f_(B)) comprise frequenciesbetween 0.2 f_(B) and 0.8 f_(B).
 15. The RF amplifier of claim 12,wherein the first packaged impedance transformer is configured toincrease an impedance to 50 ohms.
 16. The RF amplifier of claim 12,wherein the RF amplifier comprises a Doherty amplifier, and wherein thefirst transistor is a carrier transistor in the Doherty amplifier, andwherein the RF amplifier further comprises: a second transistorconnected to a second output trace of the printed circuit board, whereinthe second transistor is a peaking transistor in the Doherty amplifier,and wherein the second transistor includes a second transistor output; asecond output matching network coupled to the second transistor outputthrough the second output trace, the second output matching networkincluding a second packaged impedance transformer mounted to the printedcircuit board, and wherein the second packaged impedance transformer hasa second effective bandwidth; and a second reflection absorptioncircuit, the second reflection absorption circuit coupled between thesecond transistor output and the second packaged impedance transformerand configured to absorb reflected second signal energy from the secondpackaged impedance transformer, wherein the second reflection absorptioncircuit includes a second capacitor and a second inductor coupled to thesecond output trace of the printed circuit board.
 17. A Doherty radiofrequency (RF) amplifier configured to amplify RF signals having afundamental frequency (f₀) and a baseband frequency (f_(B)), the RFamplifier comprising: a divider configured to receive the RF signals andto divide the RF signals into first and second RF signals provided at afirst divider output and a second divider output; a first transistorcoupled to the first divider output, wherein the first transistorincludes a first transistor input and a first transistor output, andwherein the first transistor is a carrier amplifier in the Doherty RFamplifier; a first output matching network coupled to the firsttransistor output, the first output matching network including a firstimpedance transformer, the first impedance transformer having a firsteffective bandwidth; a first reflection absorption circuit, the firstreflection absorption circuit coupled between the first transistoroutput and the first impedance transformer and configured to absorbreflected first signal energy from the first impedance transformer,wherein the first reflection absorption circuit comprises a firstbaseband termination circuit and a second baseband termination circuitin parallel with the first baseband termination circuit; a secondtransistor coupled to the second divider output, wherein the secondtransistor includes a second transistor input and a second transistoroutput, and wherein the second transistor is a peaking amplifier in theDoherty RF amplifier; a second output matching network coupled to thesecond transistor output, the second output matching network including asecond impedance transformer, the second impedance transformer having asecond effective bandwidth; a second reflection absorption circuit, thesecond reflection absorption circuit coupled between the secondtransistor output and the second impedance transformer and configured toabsorb reflected second signal energy from the second impedancetransformer; and a combiner, the combiner coupled to the firsttransistor output and the second transistor output.
 18. The Doherty RFamplifier of claim 17, wherein the first impedance transformer comprisesa first packaged impedance transformer mounted to a printed circuitboard and wherein the second impedance transformer comprises a secondpackaged impedance transformer mounted to the printed circuit board.